Process for the oxidation of organic sulfides



,- rrr -2 2.=. 44,. PROCESS ron rnn OXIDATION OF ORGANIC David W. Goheen and William M, Heat-on, ;C am as ,-Wash., r

and JonasKamlet, New York, NX assignors to. C rown ZellerbachCorporation, San Francisfco, Caliii, a :oor-

poration of Nevada I p p V,

' No Drawing. Application July 16,1953

. Serial No. 148,186

m ins. (Cli zen-4601 This invention relates/to a process for theoxidation ,of organic sulfides. Moreparticularl-y, this inventionrelat'es; toa cyclic process for the oxidation of organic sulfides inthe liquid phase to the,corresponding sulfoxides,

employing nitrogen-te trc xide as an oxidant, whereby the nitrogentetroxi'de is-reduced to nitrogen trioxide and thereafter converted backtolnitrogen tetroxide' .for. subsequent reuse, and the organic sulfoxideformed:.is separated frorn the reaction mixture. JInasmuchasthenature ofthe process of the present invention is'snoh-as to produceacertainamount of;the corresponding sulfone, as a readilyrecoverableproduct in the formationof the organic ,sul'fo dde, thepreparation. of organic sulf on es is similarly claimedandcontainedwithin thescope of this invention.-

The vapor-phase oxidation of dimethylsulfide to dimethyl sulfoxidewith-an oxygencontaining .gas in the presence of a catalytic amount of anitrogengas has been described by Smedslundin US. Patent No. 2,581,-

050 (Jan. 1, 1952) and in U. S. Patents Nos. 2,825,7445

(March 4, 19:58). Wetterholrn andFossan (US. Patent 2,925,442 nifid geielfi, 1960 Ins This .nitric in in o is poorly soluble in organicsolvents; because of its very low boiling point, it v lat 'zes'immediately and is difficult to recover and racycl p in thefpr oce s s.it is also an essential feature of this process that at least one moleof N204 be employed r t o ssv lsm o a se c. s l x d z Thus the 15 2 53dq di 293 .(la t u ihs -to 2 :10). lnhish reg d s sl'vedsin, h 'p at i,solvent a d' f r he ea ter a v s' tab s ;N204- ,(.b After theaoxidationis completed, the solutionbf N 0 n the'jiner t organic solvent is;,di'st1 distillate .is condensed, in t he- ,pnes ence. of oxygen oran; oxygen-containing gas present in or introduced Qinjto the nde sinsse he o y n-c ntain n g s-(wh m rh i s qx n i .m tur o x en and a omixtures of oxygen with other inert gases suchascarbon tm zids. c rb ndio h u d s..p s n vin 41 a v a le .s s sm q..- .gnv the N2 3 su ,sta. ay sc s s t N2O4- ox e -c n ini g sa l a abs Prs s -tin t e irssb d ar os d 0 aseryes l may'i s-mb d'w hh d s llat w ile. i l; nt s qtpha aq ,main duced ntc e dis i ate p i jdn n 0 si uen h .c d n t on th rc t 'Throx f a io frhet zost w N204..-i

lr p p ari r ubst nt all .suant ta ivea t a n temxpsratu oftb di t lla oand-cond s t on h e- Noi-2j702j824-(-February 22, 1955),)havedescribedfthe liquid-phase oxidation of dialkyl sulfides to thecorresponding dialkyl sulfoxides with an oxygen-containing gas in thepresence of a catalytic amount of a nitrogen oxide. "Breach of theseprocesses the nitrogen oxide is employed only in catalytic amounts inconjunction with oxygen or air.

It is the general object of the'present inventionto pro- -:vide an,economical and commercially attractive. oyclic process 'for theoxidation of organic sulfides in the liquid 'phase'to the correspondingsulfoxides and sulfones using nitrogen tetroxide asthesole oxidizingagent,'which,is'

7 reduced to nitrogen trioxideythelatter being readily regenerated tonitrogen tetroxidefor reuse in the oxidation 'of further quantities oforganic, sulfides.

Other objects of this invention will be apparent to those skilled in theart from the following disclosure.

The basis of our invention may best be understood by a seriatimdescription of 'the various steps thereof:

(a) The organic sulfide is added to a solution ofnitrog gen tetroxide (N0 in an'inertiorganic solvent for said N 0 the amount of organicsulfidebeingnot in excess of the equivalent of one mole o' f sulfurpresent as a thioether linkage in theorganio sulfide for. eachinole 'ofN 0,. two thioether groups in=themolecule not more than onehalf mole ofsaid organic sulfide is added to each mole of N 0 dissolved in vsaidorganic solvent. The N 0 will thereupon readily oxidize thethioether group to the corresponding sulfoxidegroup ingoodyieldfandtwill' itself be reduced-to nitrogen trioxide (N20 whlchre- Thus, in the case of organic sulfides containing -tetrox-ide and isinert to chemical reaction" therewith may be used in the processo'f'thisinvent ion. Suehisolvrits j include saturatedaliphatichydrocarbons, .such as petromains dissolved in the inertorganic solvent. {'It is-anessential feature-of-the processofthisinvention'that the organic sulfide be added to the solution of the N 01n the organic -solvent, li -the reverse addition-1s efiected (i.e. .N Qsolution added to the organic sulfide), the N 0; isreduced as rapidly asadded-to nitric-oxide S recov d tsplut snpfith de ed th ma te t e oxid su on or an s h en s qu n ita v ly egenv. p the. org nic vs l rate. d';ecov r d-M chea v used continuouslyyforthe oxidation of successivebatches It should therefore :be -empha'sized, that, whereas theprocesses, ofismedslund and of Wetterholm and:Fossan (cited .;above).ernploy nitrogen oxid'es 'in catalytic ;amounts;.orily, in the presenceof greater than stoichiometrictamountsof oxygen,.the process of thisinvention employs nitrogen tetroxide as";the actual oxidant, -in

quantities at least stoichiometrically equivalent .to theorganicsulfide. Theorganic' sulfide actuallynever comes in contact withthe oxygen. ,The regeneration of the oxidant N 0 solutionis etfectedin aseparate step, discrete from the sulfide oxidation jstep. Moreover, the

1 cited prior art processes may use any nitrogen oxide ,processofthisinvention is specifically limited to the use I ,ofqN O in an inerto'rganicsolvent as the non-catalytic (e.g. 7N0, N0 N 0 etc.),.asthecatalyst ghereasthe oxidizing agent, thereby. preventing formation offree NO during the reaction.

Thejproc'ess of this invention is applicable to the oxidation of dialkylsulfides (Where .the t'woalkylrgroups- ,arethe same ordifferentLalkylaryl sulfides, diarylsulfides, alkylarallcyl sulfides,alkylalkarylsulfides, diaralkyl sultfides,.;.homocyclic and,heterocyclicsulfides and the variouslsubstit-ution products thereof,to-the correspond ing sulfoxides. Similarly, the process of thisinvention is applicable to the conversion of organic sulfides con--taining two or more thioether. groups in the-molecule,

,to the -corresponding organic diand poly-sulfox'idesf Any organicsolvent which will dissolve'nitrogen leum ether, ligroine,;Skellysolvesolvent, Stoddard solvent, hydrogenated gasoline, kerosene, ,mineraloil, white oil, solvent naphtha, etcx, theirlhalog'enated derivatives,such asmethyl chloride, methylene 'dichloitide 'chlorofo'rin,

carbon tetrachloride, methyl bromide, --dichlorodifl uoromethane, etc;aryl and alkylarylhydrooaibons, such as 'benzeneftoluene, xylene, etc';;a nd their halogenated I derivatives; such as chlorobenzene,bromobenzene, chloroa a d. th

cy e. an m y e e-f other than atmospheric pressures.

3 toluene, etc. The preferred tetroxide in the process of the presentinvention are saturated chlorinated aliphatic hydrocarbons, particularlymethylene dichloride, chloroform and carbon tetrachloride. It should benoted, however, that the boiling point of the organic solvent employedshould be below that of the organic sulfoxide formed during the reactionin order to insure an easy separation of the solvent from the mixture.

Although other solvents, such as the unsaturated aliphatic ketones (e.g.acetone) will dissolve N they are unsuitable for use in the instantprocess since the N 0 will react with such solvents causing considerabledecomposition, degradation losses of the reagent and solvent during therecovery and regeneration of the oxidant. V

In the process of this invention, a certain amount of the correspondingsulfone is obtained as a concomitant product in the oxidation of thesulfide to the sulfoxide. After distilling off the N 0 and organicsolvent, the residual organic sulfoxide and organic sulfone may bereadily separated by a single distillation and fractionation, sincethese two products usually have widely separated boiling points atnormal and reduced pressures;

The first step of the process of this invention may be effected over awide range of temperatures, e.g. from 'as low as minus 30 C.- to as highas the boiling point of the solvent for the nitrogen tetroxide at theambient pressure. The second step of the process (i.e. the distillationand regeneration of the N 0 solution in the condenser) is efiected, ofcourse, at and below the boiling point of the solvent employed at theambient pressure.

Both steps of the process may be effected at subatmospheric,

atmospheric or superatmospheric pressures. However, no practicaladvantage is gained by working at Thus, employing a solvents fornitrogen chlorinated hydrocarbons (e.g. trichloroethylene) or thesolution of N 0 in methylene dichloride, chloroform or carbontetrachloride, we prefer to effect the first step of the process (i.e.the oxidation of the organic sulfide) at atmospheric pressure at atemperature of 10" C. to 30 C. The second step of the process is thenefiected by distilling ofi' the N 0 and the solvent at atmosphericpressure (e.g. at 4041 C. in the case of methylene dichloride), andthereafter condensing the solvent at a temperature below its normalboiling point in the presence of an oxygen-containing gas whichregenerates the oxidizing solution.

The oxidation of the organic sulfide to the sulfoxide and the sulfone isvery rapid and is usually complete in 2 to 5 minutes. The combinedyields of organic sulfoxides and sulfones are very good, usually above90% of theoretical.

As pointed out hereinabove, it is essential and critical that the N 0 beemployed in the presence of an inert organic solvent. The organicsulfide may be added as such, without prior solution in the said solventor it may be dissolved in the solvent (preferably the same solvent withthe oxidizing solution. The latter procedure may be found desirablesince it helps to dissipate the heat of the reaction, to dissolve thereactants and the reaction products, and to dissolve the N 0 and the N 0during the regeneration and recovery of these compounds.

The reactions of the organic sulfides with the N 0 v Thus, it may beused to oxidize dimethyl sulfide to dimethyl sulfoxide. Dimethylsulfoxide has a wide range 'as that employed for the N 0 prior to itsadmixture of applicability as a solvent, in the manufacture of syntheticfilms and fibers, in the manufacture of paint and varnish removers, inthe formulation of resin, wax and lacquer products, as a medium for gasrecovery and separation, as a softener-and humectant for cellulosicmaterials, as a reagent, reaction medium and diluent and for a host ofother uses. The dimethyl sulfone formed by the process of this inventionmay be used as a solvent, chemical reagent and intermediate, as a dieselfuel additive, for selectivegas separation, et cetera. Thisprocess maybe also used to prepare methyl ethyl sulfoxide, methyl n-propylsulfoxide, diethyl sulfoxide, 'methyl benzyl sulfoxide, tetramethylenesulfoxid'e, pentamethylene sulfoxide. and a host of other organicsulfoxides and sulfones from the corresponding organic sulfides.

Thus, the process of this invention may be used to con vert the methylhigher-alkyl sulfides to the corresponding methyl higher-alkylsulfoxides (e.g. methyl decyl sulfoxide, methyl dodecyl sulfoxide)described by Webb in 'U.S. Patent No. 2,787,595, issued April 2, 1957,as being effective surfactants and detergent actives. Similarly,

this process may be employed to convert the alpha, deltadi-thioethers(obtained by the catalyzed reaction of dimethyl disulfide with olefinichydrocarbons) to the corresponding di-sulfoxides (e.g.3-n-decyl-2,S-dithiahexanebis-2,5-dioxide) described by Proell in US.Patent No. 2,658,038, issued November 3, 1953, as effective surfactants.

The sulfoxides obtained by the process of this invention maybe analyzedby the method described by Ligault and Groves in Analytical Chemistry,29, 1495-6 (1957).

Obvious modifications will occur to any person skilled in the art.

Example 1 In a three-necked flask equipped :with an agitator,

dropping funnel and reflux condenser fitted with a drying tube andconnected to a Dry Ice trap, was placed 18.4 gms. N 0 (0.25 mole) in 60cc. chloroform. While the temperature was held at about 20 C., a totalof 12.4 gms. of dimethyl sulfide (0.2 mole) in20 cc. chloroform wasadded in four portions, with good agitation, taking about 2 minutes forthe addition. The reaction mixture was stirred for an additional 2minutes after the addition was completed and the solventand N 0 werethen distilledoff. A stream of oxygen was passed through the condenserduring the distillation. Any gases not condensed were passed through theDry Ice trap and the condensed products were returned to thedistillation flask for a second passage through the condenser. Theresidue after the distillation was fractionated under reduced pressure.The fraction distilling at 74 76 C. at 14 mm. Hg comprised 12.9 gins. ofdimethyl sulfoxide (82.5% yield).

. The fraction distilling at about 118 C. at 14 mm. Hg

comprised 1.5 gins. of dimethyl sulfoxide mixed with dimethyl sulfone(8.0% yield).

The distillate of chloroform containing regenerated 'N O was treatedwith an additional 12.4 gms. of dimethyl Example 2 The procedureemployed in Example 1 was repeated at 10C. and using carbontetrachloride as a solvent. Us-

7 ing a two minute addition time and additional agitation for twominutes, gave (from 18.4 gins. N 0 in 60 cc. carbon tetrachloride and12.4 gins. dimethyl sulfide in 20 cc. carbon tetrachloride) thefollowing yields:

- 13.1 gms. of dimethyl sulfoxide (84.0% yield) 1.2 gins. of dimethylsulfone (6.4% yield) In each case, the procedure was repeated with the areevered' and regenerated In a reaction flask similar. that ern 1 wasplaced 6.9 guts. of N20,; (0.075 mole) in 40 cc.

loyedin Example 1 -iehiavjaat atmosphericgpressure, no oxygen-wasfintroduce d. The yields=weref Q in 30 cc. chloroformwas,addedtdropwise,-with;goodiagitation, over a period of .30 minutes,wyliilelmaintaininglthe temperature at .22''-'24'" C. The "solvent and:oxidant were recovered and regenerated as-in Example 1. On fraction--:ation under reduced ,pressure, :19.5-;gms. of methyl .octyl 'wereobtained.

" good agitation'over a period of anhour,"

sulfoxide (80% yield) was recovredat 130- -1'34C. /.2

mm. Hg and about 2.0 gms. of methyltoctyl-sulfone (about 14%) could berecovered from residue. r p

On repeating the oxidation'with 'therec'overed'a'nd regeneratedoxidizing solution, substantially ,thes'ame yields In a reaction flask"('l).2 5"inole in 100 cc.

1 'was :placed 23.0 gms. N

chloroform. 15.5 gms. of. .100 cc. chloroform was maintained at slightlybelow 25':C.":by.means' of fan ice-bath. The re'actionmixture was-stirred foran additional few rmnutes and "the solventand-N o wereremoved by distillation. On fractionation under'reduced pressure, therewere recovered 17.15 ,gmsEiofdimethyl isulfoxide (88.01% yield) a d 1:7;ofdimethylisulfone f;[(9-0% yield).

The procedure employed in Example-4 was repeated, :maintainingthetemperature during the oxidation-at 30 C. .From 18.4 gms. of N 0 I 80cc. of carbon tetrachloride,- there were obtained V .13.0. g ms.of,dimethylsulfoxideit835%..y l 2.9,.gms. of dimethyllsulfone {115.5%yield-)5 v Q '.""Sub'stantial1y identical yields were jammed with therecovered and regenerated oxidizing solution.

Example .6

In areactionfiask similar to that employed imExample Z1116shighBr-boiling still dimethyl: sulfide (0:25 .rnole) in added "thereto.dropwise, with 1 The temperature 112.4 gmsdi eflirl snare (19. yiel 2.5idir'nethylasulione (13.3% yield) Since adaxygen' was introduced, ire-N9. was formed .duringrconcentration and thus non was sarried' backy-intoth fl k rreflux aa qlvsat anincmsed 1 ,.oxide yield-and. adecrea ed s nyi d we e obta ned.

In a reaction flask' to thatemployed in Example i 1, 184 gms. of N Owfl-rmole in 60 cc. carbon tetra- :ych o z d w (p aced. an all sgm -rime l d 15 i dr s p n' wtare at -0-5 C." :fI 'he reaction mixture wasagitated for 30.n1inlltes egsqlventgand N 0 were then distilled pit;[and the residue fractionated. :There were thus mole): addedovera 51minLohtained. a 1.

j, "1.9 gms of Thus the use of this lower temperature range and longerreaction periodgives'no increase in sulfoxide yield.

T areaction-flasl; similar'to thatemployed in Example 1 was placed 118:4gmss' of"iNO4 (-0 .-2"mole) in cc.

of methylene dichloride. iliojthissolution 12.4 gms. of diadded over atwo minute period at 1 a-temperaturegma ntained at 20" C. After .1116

mixture 'w'assti'rr for janadditional'zfminutesat ZOifC the solvent andN203.werefdistilledjofi atatmospheric .aa g s due f ac i n ted t osgg'dime rl ,su1 f. inel;( 1-2% y el 'lfherecovered and.regeneratedoxidizing solution was reused repeatedly tooxidizeeight'successive batches of I olita'ined'in each-case, #5 rtetrachloride and, 'over' a period of two-minutes, while maintaining thetemperature at -20f-' (3.; there-was f added 12.4 gms. of dimethylsulfide flklm'ole) with no solvent;

' The reaction mixturewas stirreda'two minutesfahftercompletion ofthe'-,-addition and' the solvent and-N 0 were "then removed atthe'Water-p'ump, The-N 0 wasoxidized *t'o N O -in the same manner' asc'lescribed in Example 1.

The residue on distillation, gave:

This experiment was thenirepeated.exceptthat the solvent and N 0 were Iremoved: at-;atmospheric pressure and oxygen was admitted ito-thecondenser-mower to oxidize the N Q 1back toN Q -v2lhe yieldsiw erez 11.5gins. (ii-methyl sulfoxidef(.73.7.% .yield) 4.2 gms. dimethyl sulione;(;22.3,%.- yield) Theyieldof sulfoxide'was reduced iandthat' fd f thesulio-ne was increaseddue'to the fact'thart some -of'the regenerated N 0was carried back into; the. oxidation flaslg by reflux-""ingsolvent'cluring thedi's't'illation. f'Theioxygenjwas adnnittedthrough the'thermorne'terwell dfia Claison-type *distillationhead.

" "-I"hc'e*solve'nt andregenerated hl figyvere eactedfagain With 12.4gms. dimethyl sulfide 'and"tlre solvent"wasagain Examples 9-15 T p e remp oye i Exampl 7 8' s rep to :oxidize the; following..0rganic]sulfidesto the corresponding sulfox'ides in the stated yields ram ar s 1 jInorder vto determinethe eli'ect.oi distillingvco'ff the .,N2O3 and thesolvent at varying pressures; a solution containing o olemfNzqri nrthtform fr a s uti n carhonzt r ch contain ng 167% N2Q4ran -83 was cooledto minus 10 C.,and'one mole of dimethyl sulfide was added, withgoodagitation, permitting the ,temperature to rise to 30" ,C.,duringthe. addition; The jIIiQggand carbgn tetrachloride. were thenremove'dby distilling under reduced pressures atd ifieiyentTte'rrig'aerh112.1as.amennewreinstall) j] y g and analyzing 92.4% methyl dodecylsulfoxide.

7 tom ranges (at 10 C. intervals) between 30 and 78C. The followingyields were obtained:

Dirnethyl sulfoxide, percent; 70 i 82 Dirnethyl sulfone, percent-.- 3 6In each case, the oxidizing solution of N O in G01 could bequantitatively regenerated by the introduction of oxygen into the,condensing vessel.

' 1 Example 17 Methyl dodecyl sulfide was prepared by'the reaction ofmethyl mercaptan with propylene tetramer in the preswhile maintainingthe temperature at 25 C; The reactionvmixture Was agitated'for'a furtherfive minutes, and the N and solvent were then distilled off andregenerated in the same manner'as described in Example 1.

The residue in the still solidified on cooling to a crystalline whitesolid, M.P.=5054 C., weighing 43.6 gms.

, Example 18 temperature at 25 C. The reaction mixture was agitated fora further five minutes and the N 0 and solvent were then distilledoffand regenerated.

The residue in the still solidified on cooling in the re frigerator to asolid, M.P. 25-28 C., weighing 26.6 gms. and analyzing 88% of3-n-decyl-2,5-dithiahexanebis-2,5-sulfoxide.

Example 19 In a reaction flask similar to that employed in Example 1,18.4 gms. of NO (0.2 mole) in 60 cc. of Skellysolve solvent (B.P. 69-96C.) was placed, and 12.4 gms. dimethyl sulfide (O.2 mole) added over aperiod of about 3 minutes, keeping the temperature at about 20 C. Themixture was stirred for 3 minutes, the solvent and N 0 were thendistilled oil at a reduced pressure at the Water pump, and the residuewas fractionated. The yields were:

13.3 gms. of dimethyl sulfoxide (85.2% yield) 1.6 gms. of dimethylsulfone (8.5% yield) Example 20 In a reaction flask similar to thatemployed in Example 1, 18.4 gms. of N 04 (0.2 mole) in 60 cc. of xylenewas placed, and 12.4 gms. dimethyl sulfide (0.2 mole) added. Thereaction conditions, distillation of the solvent-N 0 solution andfi'actionation of the residue were the same as in the Example 19. Theyields were as follows:

10.1 gms. of dimethyl sulfoxide (64.8% yield) 3.8 gms. of dimethylsulfone (20.2% yield) Example 21 Following again the procedure describedin Example 19, to 18.4 gms. of N O.; (0.2 mole) in 60 cc. of chloro-.benzene there wasadded 12.4'gms. of dimethyl sulfide (0.2 mole).Theyields'were: I V L 12.6 gms. of dimethyl sulfoxide (80.8% yield) gms.of dimethyl sulfone (7.8% yield) Example 22 i Ina reaction flask similarto that employed in Example 1 was placed 46 gms.-N (0.5 mole) in 150 cc.

chloroform. 15.5 gms. of dimethyl sulfide (0.25 mole) in 100 cc.chloroform was added thereto dropwise with stirring over a period of 5minutes. The temperature was allowedto rise to the boiling point of thereaction mixture. The reaction mixture was stirred and refluxed for 75minutes, and thereafter the N 0 and chloroform were distilled oil. Theyields were:

5.2,gms..of dimethyl sulfoxide (26.6% yield) 14.9 gms. of dimethyl sulfone (63.0% yield) The above examples clearly illustrate the presentinvention and it will be obvious to' those skilled in the art that otherorganic sulfides and organic solvents for nitrogen tetroxide than thosedescribed in the above examples may 'be employed.

- Having thus' described our invention, we claim;

1. A process for the oxidation of organic sulfides which comprisesthesteps of:

to a solution of nitrogen tetroxide (N 0 in an inert organic solvent forsaid nitrogen tetroxide, in an amount equivalent to at least one mole ofnitrogen tetroxide for each mole-equivalent of sulfur present as athioether linkage in said organic sulfide, oxidizing the organic sulfideto the corresponding sulfoxide and reducing the nitrogen tetroxide tonitrogen trioxide (N 0 (b) distilling off the nitrogen trioxide and theinert organic solvent and condensing the distillate in the presence ofan oxygen-containing gas in quantity at least sufiicient to convertsubstantially all of the nitrogen trioxide to the nitrogen tetroxide andthereby regenerating the oxidizing solution of nitrogen tetroxide in theorganic solvent, and

(c) recovering the organic sulfoxide formed from the residue of thedistillation, the boiling point of said organic solvent being below theboiling point of the sulfoxide formed during the reaction.

2. The process of claim 1 in which the inert solvent for the nitrogentetroxide comprises a saturated chlorinated aliphatic hydrocarbon.

3. The process of claim 1 in which the inert solvent for the nitrogentetroxide comprises at least one member of the group consisting of thesaturated aliphatic and aromatic hydrocarbons and the saturatedhalogenated aliphatic and aromatic hydrocarbons.

4. The process of claim 1 in which the inert solvent for the nitrogentetroxide is methylene dichloride.

5. The process of claim 1 in which the inert solvent for the nitrogentetroxide is chloroform.

6. The process of claim 1 in which the inert solvent for the nitrogentetroxide is carbon tetrachloride.

7. The process of claim 1 in which the corresponding organic sulfoneis'recovered from the oxidation product after the separation of theorganic sulfoxide.

8. The process of claim 1 in which the oxidation of the organic sulfideby the nitrogen tetroxide in the organic solvent is effected at a.temperature between minus 30 C. and the boiling point of the solvent atthe ambient pressure.

9. The process of claim 1 in which the distillation and regeneration ofthe oxidizing solution of the nitrogen tetroxide in the organic solventis efiected at a temperature not in excess of the boiling point of saidsolvent at the ambient pressure.

10. The process of claim 1 in which the oxidation of the organic sulfideby the nitrogen tetroxide in the organic solvent is effected at atemperature between 10 C. and

30 C. a v

11. The process of claim 1 in which the oxidation of the organicsulfide, the distillation and the regeneration of the oxidizing solutionof the nitrogen tetroxidein the organic solvent is effected atatmospheric pressure.

12. The process of claim 1 in which the oxidizing solution of nitrogentetroxide in the organic solventis 'regenerated by the introduction ofoxygen.

13. The process of claim 1 in which the oxidizing solution of nitrogentetroxide in the organic solvent" is regenerated by the introduction ofair.

14. The process of claim 1 in which. the organic sulfide is dimethylsulfide and the organic sulfoxide is dimethyl sulfoxide.

15. The process of claim 7 in which the organic sulfide is dimethylsulfide and the organic sulfone is dimethyl sulfone.

16. The process of claim 1 in which the organic-sulfide is methyl octylsulfide and the organic sulfoxide is methyl octyl sulfoxide. p 7

17 The process of claim 1 in which the organic sulfide is methyl dodecylsulfideand the organic sulfoxide is methyl dodecyl sulfoxide.

18. The process of claim 1 in which the organic sulfide is3-n-decyl-2,S-dithiahexane and the organic suit-- oxide is3-n-decyl-2,5-dithiahexane bis-2,5-sulfoxide.

fractionation, and

7 19. A cyclic process for the manufacture of dimethyl sulfoxide anddimethyl sulfone which comprises the steps of: r

(a) adding dimethyl sulfide to a solution of nitrogen tetroxide 1nmethylene dichloride, the quantity of dimethyl sulfide being not inexcess'of one mole for each vmole of nitrogentet'roxide employed, toform nitrogen trioxide and a mixture of dimethyl sulfoxide with a minoramount of dimethyl sulfone;

(b) distilling ofi the resultant solution of nitrogen trioxide andmethylene dichloride and condensingsaid distillate in the presence of anoxygen-containing gas in quantity tsufiicient to oxidize substantiallyall of the nitrogen trioxide to nitrogen tetroxide;

' '(c) recovering the dimethyl sulfoxide and the di-' methyl sulfonefrom the residue of said distillation by (d) recycling the oxidizingsolution of nitrogen tetroxide in methylene dichloride regenerated instep (b) of said process to step (a) of said process.

' References Cited in the file of this patent UNITED STATES PATENTS2,702,824 Wetterholm et a1 Feb. 22, 1955 Smedslund Jan. 2, 1952'

1. A PROCESS FOR THE OXIDATION OF ORGANIC SULFIDES WHICH COMPRISES THESTEPS OF: (A) ADDING AN ORGANIC SULFIDE SELECTED FROM THE GROUPCONSISTING OF DIALKYL, ALKYLARYL, DIARYL, ALKYLARALKYL, ALKYLALKARYL,DIARALKYL, HOMOCYCLIC, HETEROCYCLIC AND AT LEAST TWO THIOETHER GROUPS INTHE MOLECULE-CONTAINING SULFIDES TO A SOLUTION OF NITROGEN TETROXIDE(N2O4) IN AN INERT ORGANIC SOLVENT FOR SAID NITROGEN TETROXIDE, IN ANAMOUNT EQUIVALENT TO AT LEAST ONE MOLE OF NITROGEN TETROXIDE FOR EACHMOLE-EQUIVALENT OF SULFUR PRESENT AS A THIOETHER LINKAGE IN SAID ORGANICSULFIDE, OXIDIZING THE ORGANIC SULFIDE TO THE CORRESPONDING SULFOXIDEAND REDUCING THE NITROGEN TETROXIDE TO NITROGEN TRIOXIDE (N2O3), (B)DISTILLING OFF THE NITROGEN TRIOXIDE AND THE INERT ORGANIC SOLVENT ANDCONDENSING THE DISTILLATE IN THE PRESENCE OF AN OXYGEN-CONTAINING GAS INQUANTITY AT LEAST SUFFICIENT TO CONVERT SUBSTANTIALLY ALL OF THENITROGEN TRIOXIDE TO THE NITROGEN TETROXIDE AND THEREBY REGENERATING THEOXIDIZING SOLUTION OF NITROGEN TETROXIDE IN THE ORGANIC SOLVENT, AND (C)RECOVERING THE ORGANIC SULFOXIDE FORMED FROM THE RESIDUE OF THEDISTILLATION, THE BOILING POINT OF SAID ORGANIC SOLVENT BEING BELOW THEBOILING POINT OF THE SULFOXIDE FORMED DURING THE REACTION.